1. FIELD OF THE INVENTION
This invention relates to photographic sensitive materials of improved photographic characteristics (for example, reduced fog). Particularly, it relates to color photographic sensitive materials in which abnormal coloration of a silver halide photographic emulsion layer is inhibited by incorporating into the surface layer thereof a polysiloxane containing a polyoxyalkylene chain in its side chain.
2. DESCRIPTION OF THE PRIOR ART
In photographic sensitive materials, one side or both sides of a support are coated directly or via a subbing layer with a sensitive photographic emulsion layer, and, if desired, further other layers such as an intermediate layer, protective layer, filter layer, antistatic layer and the like can be provided. As the support, .alpha.-polyolefin films such as polyethylene films, polystyrene films, cellulose ester films such as cellulose acetate films and cellulose nitrate films, polyester films such as polyethylene terephthalate films, paper or paper sheets coated with such film materials are used. Though in direct X-ray films both sides of the support are coated with a photographic emulsion, in most photographic sensitive materials only one side of the support is coated with a photographic emulsion. Accordingly, in the latter case there remains a side not coated with a photographic emulsion, that is, the surface of the support which is called the "back face" in this art.
In some sensitive materials, auxiliary layers are provided on the back face such as a halation preventing layer, an antistatic layer, an adhesion preventing layer, a curl preventing layer, an overcoat layer and the like in order to improve the photographic or physical properties of the photographic sensitive materials.
During handling of the materials, e.g., winding, rewinding, carrying upon photography, development, printing or projection as well as during manufacturing steps such as coating, drying and processing, photographic sensitive materials are often harmed by contact friction between the sensitive materials and various apparatus, machines and cameras due to contact therewith or due to friction or adhesion between photographic sensitive materials, namely, between the surface and the back face of the photographic sensitive materials. For example, there can occur scratches at the surface or back face of the photographic sensitive materials, a worsening of the ability to drive the sensitive materials in a camera and other machines and a stripping of the photographic layers from the photographic sensitive materials due to poor adhesion.
Recently, changes in methods of use and treatment of sensitive materials (e.g., high speed photography and high speed treatment) and diversified circumstances of use, e.g., under high temperature and high humidity conditions, have imposed more severe handling conditions upon sensitive materials than in the past, and, as a result, contact friction and adhesion troubles are now even more likely to occur, particularly at the surface of the sensitive materials.
For example, one serious problem caused by adhesion appears in color photographic films. In forming color photographic images there is generally used a color developing method which comprises reducing silver halide particles in an exposed photographic emulsion with a developing solution containing an aromatic primary amine as a developing agent, particularly an N,N-di-substituted-p-phenylenediamine compound, and reacting the oxidized product of the developing agent with various couplers to thereby form cyan, magenta and/or yellow dye images. As the couplers for such a color developing method there are generally used compounds which contain a phenolic hydroxy group, anilino amino group or an active methylene group and which form a dye that absorbs light of a certain region of the visible wavelength upon oxidative coupling with the aromatic primary amine developing agent.
When color photographic films, particularly those for motion pictures, are stored for long times under high humidity while tightly wound, adhesion between the back face and the surface of the color photographic film often takes place, and abnormal coloration shows up, particularly in the outermost photographic emulsion layer when the adhered films are separated and developed. For example, when a photographic emulsion layer containing in a blue sensitive photographic emulsion a coupler forming a yellow dye on coupling with a developing agent (e.g., of the p-phenylenediamine type) during development is provided at the top of the photographic emulsion layers, it colors yellow without exposure. This coloration makes the color picture obtained after processing indistinct to a great extent, and lowers the value of the film. Although the cause of this undesirable phenomenon has not yet completely established, it is believed that electrostatic charges are created on the surface of the film when adhered film sheets are separated which are hard to dissipate and which accumulate because of the poor conductivity of the photographic film, whereby the photographic emulsion is sensitized by static electricity discharge which accumulates beyond a certain limit. In this case, it is possible that the photographic emulsion will be sensitized by the light caused by the spark discharge or that the photographic emulsion will be sensitized by electric action due to electron streaming of a certain amount of the static electricity in the photographic emulsion. When the photographic emulsion is sensitized without exposure and blackening appears on development, this is called fogging in this art. Branch-like, feather-like or spot-like black images appear on the film after development when the photographic emulsion is sensitized, particularly by spark discharge due to static electricity, and these black images are called static marks.
In the case of using color sensitive materials, blackened silver does not remain in the sensitive materials since a bleach-fixing is conducted, but the coexisting coupler colors upon development.
In order to prevent such undesirable coloration due to fogging, the following methods have been used. One method eliminates the generation of static electricity. Since the generation of static electricity is caused by stripping adhered films, it can be stopped by decreasing the adhesiveness and adherence of the surfaces of the photographic materials, i.e., it is important to reduce the adhesiveness between the photographic emulsion layer surface and the back face. Another method is to impart to the photographic sensitive materials an antistatic capability, thereby reducing static charges.
Many techniques are known within these general methods. As examples of the former method, there is known a method which comprises dispersing in the surface layer of a photographic material a forming agent which forms projections, generally called a matting agent, such as inorganic compounds (e.g., silver halide, silica, barium strontium sulfate) and polymers (e.g., polymethyl methacrylate particles) to thereby make the surface layer coarse; a method which comprises incorporating in the surface layer of the sensitive materials a lubricant such as a liquid paraffin, a higher fatty acid ester on dimethylpolysiloxane, to thereby improve the frictional properties; and a method which comprises adding to a halation preventing layer of the back face a long chain carboxylic acid amide as is described in U.S. Pat. Nos. 2,732,305 and 3,433,638 to thereby prevent adhesion between the back face and the surface of the emulsion layer.
However, although these methods are effective to a certain extent to improve slippage, they are unexpectedly not effective in preventing the abnormal coloration of color photographic sensitive materials. Further, when in accordance with these methods the amount of the additives is increased to such an extent as to prevent abnormal coloration, these methods have the defects that transparency is impaired and condensates are liable to form in a coating liquid, thereby lowering the coating characteristics and imparting to the surface of the photographic sensitive material a tendency to be injured due to poor slippage. Further, transportation characteristics during coating and drying and processing are rather worsened and adhesives utilized to join photographic films are not effective because of the low sliding friction.
Further, there have been proposed methods for improving adhesion prevention by incorporating a certain kind of surface active agent in the surface layer of the photographic sensitive material, but most of these methods also have the defects that coating characteristics are worsened, photographic characteristics are worsened due to a reduction of sensitivity and the generation of fog and, further, the surface active agent's function is reduced by interaction with other additives such as antistatic agents and halation preventing agents. Further, dialkylpolysiloxane type silicone oils are known as lubricants for photographic film surfaces. For example, imparting slippage to a photographic film by the simultaneous incorporation of a dimethylpolysiloxane and a particular surface active agent into a photographic emulsion layer or protective layer is described in U.S. Pat. No. 3,042,522; imparting slippage by coating a mixture of a dimethylsilicone and diphenylsilicone on the back face of a photographic film base is described in U.S. Pat. No. 3,080,317; imparting slippage to a photographic film by incorporating into a protective layer methylphenylsilicone blocked with a terminal triphenyl is described in British Pat. No. 1,143,118; providing photographic sensitive materials having slippage and adhesion resistance by incorporating a di-lower alkylsilicone and a .alpha.-alanine surface active agent into a photographic emulsion layer or other hydrophilic colloid layer is described in U.S. Pat. No. 3,489,567; and using a polyoxyethylene adduct containing 3 silicon atoms in the molecule thereof as a coating aid is described in Japanese Patent Publication No. 34,230/70 . However, these dialkylpolysiloxane type silicone oils and fluorine oil (a polymer of monochlorotrifluoroethylene, for example, trade name "Daifloil" produced by Daikin Kogyo Co., Ltd.) are wholly uneffective to prevent the above described abnormal coloration, even if they are applied in color photographic materials to either a back layer or the surface of an emulsion layer or both of them.
Further, certain kinds of polymers, for example, copolymers of vinyl acetate and maleic acid half dodecylester and copolymers of styrene and maleic acid half heptylester are effective to some extent when applied to a back layer of a color sensitive material, but completely satisfactory effects cannot be obtained. In addition, such copolymers generate turbidity in the back layer after photographic treatment of the sensitive material, and bring about the tendency of these polymer coatings to strip from the back face and transfer to the surface of a photographic sensitive material when the surface of the photographic sensitive material and the back face are contacted under relatively high humidity and under pressure.
On the other hand, as a means for imparting antistatic characteristics, one way is to impart slippage to the surface of a sensitive material to thereby prevent the generation of static electricity, but this is not very effective. Therefore, reducing the generation of static electricity and electrification by adding an antistatic agent to the surface layer of film has generally been employed. Such a method is described in U.S. Pat. Nos. 3,625,696, 3,615,531, 3,564,043, 3,525,621, 3,457,076, 3,264,108 and 3,756,828, and most of the antistatic agents used for this purpose have characteristics which differ substantially from those of the aforementioned adhesion preventing agents dye to the hygroscopic properties of the antistatic agents.
As illustrated above, antistatic characteristics are generally incompatible with adhesion resistance characteristics. Therefore, it is very difficult to expect satisfactory effects on inhibiting abnormal coloration using conventional antistatic agents. That is to say, when a back face and a surface of a sensitive material containing such antistatic agent are contacted, adhesion tends to occur and when the adhered films are separated static charges tend to be generated more often than adhesion protection is imparted.
Although an abnormal coloration prevention effect can be expected if the generated static charges can be readily dissipated without accumulation, there are no antistatic agents which have such an excellent effect. In addition, even if such antistatic agents could be found, they would not be very effective since they would have the defects that they would render the film sticky and lower surface strength.